1. Field of Invention
The invention relates to a writing or drawing instrument with a writing tip provided at the front end which can be brought into contact with a writing or drawing pad, and with a writing fluid reservoir for supplying the writing tip with writing fluid, the volume of which is reduced as the writing fluid is used up.
2. Brief Description of the Prior Art
In a known writing or drawing instrument of this type (German Published, Non-Examined Patent Application DE-OS 20 35 526, equivalent to U.S. Pat. No. 3,737,242), the walls of the writing fluid reservoir are essentially formed by a thin, flexible foil which is deformed when subjected to small pressure loads. The writing fluid reservoir is connected by its front end with the writing tip, but otherwise is sealed with respect to the ambient air. This means that the writing or drawing instrument does not have a pressure equalization system which receives writing fluid and which is in contact with the ambient air. If writing fluid from the writing fluid reservoir, which contains practically no air, is used up, the flexible foil is deformed under the effect of the ambient pressure in such a way that the volume of the writing fluid reservoir is appropriately reduced. Thus, the ambient pressure always acts on the writing fluid in the writing fluid reservoir. Pressure increases in the writing fluid reservoir on account of the expansion of air caused by increases in temperature do not occur with this known writing or drawing instrument, because practically no air is contained in the writing fluid reservoir.
This particular writing or drawing instrument does avoid certain known disadvantages from using a pressure equalization system, such as drying out of the writing fluid in the pressure equalization system, emergence of writing fluid from the pressure equalization system into the ambient air, or considerable manufacturing expense. However, this known writing or drawing instrument has a disadvantage in that the entire static pressure of the writing fluid in the writing fluid reservoir rests on the writing tip, so that there is a danger of writing fluid dripping at the tip. Attempts to reduce or remove the danger of dripping by means of a considerable increase in the capillary forces in the area of the writing tip would reduce the drawing speed of the writing or drawing instrument. The emergence of writing fluid during the writing or drawing process is made more difficult whenever there is an increase in capillary forces.